Day 11

Author: petertseng

11_hex_grid.rb

@@ -0,0 +1,43 @@
+def dist(x, y)
+  # If move NE then SE, you end up at (1, -1).
+  # This requires 2 moves to get to, since there is no +1, -1 move.
+  # Same if we are at (-1, 1) since there is no -1, +1 move.
+  # Therefore:
+  # If both coords are same sign, distance is the maximum magnitude.
+  # If they are of different sign, distance is sum of magnitudes.
+  #
+  # NOTE that for my input, it was sufficient to always use max only!
+  # So, I never had a situation where I was [+, -] or [-, +].
+  x.positive? == y.positive? ? [x.abs, y.abs].max : x.abs + y.abs
+end
+
+
+x = 0
+y = 0
+maxdist = 0
+
+(!ARGV.empty? && ARGV.first.include?(?,) ? ARGV.first : ARGF.read).split(?,) { |i|
+  case i.strip
+  when 'ne'
+    y -= 1
+  when 'sw'
+    y += 1
+  when 'nw'
+    x -= 1
+  when 'se'
+    x += 1
+  when 'n'
+    y -= 1
+    x -= 1
+  when 's'
+    y += 1
+    x += 1
+  else
+    raise "unknown #{i}"
+  end
+  maxdist = [maxdist, dist(x, y)].max
+}
+
+puts dist(x, y)
+
+puts maxdist